G6-1.5K-SAI: a new Geoengineering Model Intercomparison Project (GeoMIP) experiment integrating recent advances in solar radiation modification studies

Abstract. The Geoengineering Model Intercomparison Project (GeoMIP) has proposed multiple model experiments during the phases 5 and 6 of the Climate Model Intercomparison Project (CMIP), with the latest set of model experiment proposed in 2015. With phase 7 of CMIP in preparation, and with multiple efforts ongoing to better explore the potential space of outcomes for different Solar Radiation Modification (SRM) both in terms of deployment strategies and scenarios and in terms of potential impacts, the GeoMIP community has identified the need to propose and conduct a new experiment that could serve as a bridge between past iterations and future CMIP7 experiments. Here we report the details of such a proposed experiment, named G6-1.5K-SAI, to be conducted with the current generation of scenarios and models from CMIP6, and clarify the reasoning behind many of the new choices introduced. Namely, compared to the CMIP6 GeoMIP scenario G6sulfur, here we decided on: 1) an intermediate emission scenario as baseline (the Shared Socioeconomic Pathway 2-4.5); 2) a start date set in the future that includes both considerations around the likelihood of exceeding 1.5 ºC above preindustrial and some considerations around a likely start date for an SRM implementation; 3) a deployment strategy for Stratospheric Aerosol Injection that does not inject in the tropical pipe in order to obtain a more latitudinally uniform aerosol distribution. We also offer more details over the preferred experiment length and number of ensemble members, and include potential options for second-tier experiments some modeling groups might want to run. The specifics of the proposed experiment will further allow for a more direct comparison between results obtained with CMIP6 models and those obtained with future scenarios for CMIP7.